Synthetic lubricants containing trimethylol - alkane - di - ortho-silicic acid esters



United States Patent O 3,514,402 SYNTHETIC LUBRICANTS CONTAINING TRIMETHYLOL ALKANE DI ORTHO- SILICIC ACID ESTERS Herbert Gothel, Oberhausen-Sterkrade, and Hans Feichfinger, Dinslaken, Germany, assignors to Ruhrchemie Aktiengesellschaft, Oberhausen-Holten, Germany, a corporation of Germany No Drawing. Filed Nov. 28, 1967, Ser. No. 686,293 Claims priority, application Germany, Dec. 1, 1966, R 44,696 Int. Cl. (310m 1/52, 3/46 US. Cl. 2 52-49.6 20 Claims ABSTRACT OF THE DISCLOSURE Synthetic lubricant esters of the disilicic acid ester type having the formula (SiDAO-Si)-(OR) ,,(OR') wherein A is a polymethylol-carboxylic acid ester of the structural formula:

CH2--CH2 wherein Z is the ester residue of said carboxylic acid and R is hydrogen or a lower alkyl of about 1 to 6 carbon atoms, R is alkyl, R' is diethylene glycol-n-butyl ether residue, R and R may be the same or diiferent, and n is to 3.

Synthetic lubricants for turbine engines must possess a number of properties in order to be capable of heavy duty service undervarying operationg conditions. They must be on the one hand fiowable at 55 C., in order to allow low temperature starting of the oil pumps at great heights. They must also withstand temperatures of 400 C. and even higher, which temperatures are reached at hot points of the engine, without undergoing thermal or oxidative decomposition.

It is known to use esters of polyvalent alcohols having a quaternary carbon atom as lubricants for jet power aircraft engines, as for instance neopentylglycol, trimethylolethane and trimethylolpropane (see, for instance, Ullmanns Enzyklopadie der technischen Chemie, vol. 15, 1964, p. 292 et seq.). These esters possess high thermal and oxidative stability, but their viscosity-temperatureresponsivity and their viscosity at low temperatures are unfavorable (see Table 1, esters A to D).

It was hitherto tried to use silicones as lubricants (see for instance Ullmann l.c., p. 295 et seq.). These compounds possess an excellent viscosity-temperature-responsivity, since they are stable at high temperatures and have low setting points, however, their lubricity is limited. It was attempted to overcome this drawback by the use of halogenated silicones, but these materials cannot be employed at high temperatures, since they are corrosive even at 260 C. (see Gunderson/ Hart, Synthetic Lubricants, p. 314).

Lubricants bases on orthosilicic and disilicic acid esters are described in Ullmann, l.c., p. 298 et seq. They also possess excellent viscosity-temperature-responsivity, but become easily hydrolized with formation of gels. Their oxidative stability is unsatisfactory (see Table II, esters 1 to 3), so that they must be stabilized by the addition of other substances. Furthermore, lubricating films of tetraalkyl-orthosilicic acid esters exhibit unsatisfactory load carrying capacities at mixed friction.

3,514,402 Patented May 26, 1970 "ice It is an object of the invention to overcome the difiiculties encountered in the art and to provide silicic acid esters suitable as lubricants which meet the requirements, i.e., satisfactory high temperature responsivity, adequate flowability at low temperature and good lubricity over a broad temperature range, without exhibiting the drawbacks of the lubricants known in the art.

Another object of the invention is to provide fluid compositions suitable for use as lubricants in jet propulsion aircrafts.

Other and additional objects will become apparent from a consideration of the instant disclosure including the claims hereof.

In accordance with and fulfilling these objects, one aspect of the present invention resides in the use of liquid materials comprising di-orthosilicic acid esters of the formula wherein A represents a radical of an ester derived from a trimethylol-alkane containing a quaternary carbon atom and having up to about 10 carbon atoms, preferably a trimethylol-alkane, and a saturated carboxylic acid having about 3 to 20 carbon atoms corresponding to the structural formula:

wherein Z is the ester residue of said carboxylic acid and R is hydrogen or a lower alkyl of about 1 to 6 carbon atoms, R represents an alkyl group having about 4 to 20 carbon atoms, R represents a n-butoxy-diethylene glycol ether radical, n has a value of 0 to 3 and wherein R and R may be the same or different, as lubricants in jet propulsion aircrafts.

The liquid compositions of this invention may be used alone or admixed with other liquid materials, e.g., conventional fluid materials suitable for use as lubricants as well as with the conventional additive materials, i.e., antioxidants, etc.

In accordance with the invention, di-orthosilicic acid esters wherein the A-groups are radicals of the monoester of trimethylolethane, trimethylolpropane or trimethylolbutane with pivalic acid, isobutyric acid or 6,5- dimethylbutyric acid constitute broadly preferred di-orthosilicic acid esters.

Di-orthosilicic acid esters, wherein R represents alkyl radicals having about 7 to 20 carbon atoms are well suited.

The monoesters of polyvalent alcohols, characterized by A in the formula given hereinbefore, can be obtained by reaction of one mole of the polyvalent alcohol and one mole of the carboxylic acid hereinbefore defined, at a temperature below about C. followed by distillative recovery of the ester thereby formed.

The starting materials for the R groups having about 7 to 20 carbon atoms may be derived from alcohols obtained by hydroformylation of straight chain olefins followed by hydrogenation.

The di-orthosilicic acid esters according to the invention have hitherto not been described. They may be prepared 'by the conventional methods employed for the production of di-orthosilicic acid esters as known in the art, as for instance by reacting stoichiometric amounts of corresponding water-free alcohols, polyoxyalkylene glycols and monocarboxylic acid esters of the polyvalent alcohols with gaseous silicon tetrachloride as disclosed in German Pat. 1,142,855 or as discolsed in German patent applica- 3 tion R 32,696 IVb/ 12 0, German Auslegeschrift 1 180 359.

The advantages and properties of the novel di-orthosilicic acid esters of the invention as lubricants are shown in the following Table I wherein a comparison of certain of the esters of the invention With certain known silicic acid esters has been set out.

The esters of the invention used in the comparison and listed in Table I are the following:

(I) trimethylolethane-monopivalate-di-orthosilicatehexa-n-nonyl-ester (II) trimethylolpropanemono-pivalatedi-ortho-silicateheXa-n-nonyl-ester (III) trimethylolpropane-mono-isobutyrate-di-orthosilicate-hexa-n-nonyl-ester (IV) trimethylolpropane-mono-pelargonate-di-orthosilicate-heXa-n-nonyl-ester (V) trimethylolethanemono-pivalate-di-orthosilicatehexa-n-octyl-ester (XII) trirnethylolpropane-mono-3,5,5-trimethylhexanoate-di-orthosilicatehexa-n-decyl-ester (XIII) trimethylolpropanemono-propionate-di-orthosilicate-heXa-n-decyl-ester (XIV) trimethylolpropane-mono-pivalate-di-orthosilicate-heXa--iso-decyl-ester (XV) trimethylolpropane-mono-pivalate-di-orthosilicate-tri-n-undecyl-tri- (diethyleneglycol-n-butyl-ether) ester Esters comapred therewith are the following dibasic esters and orthosilicic acid esters known in the art:

(A) bis- Z-ethylhexyl sebacate (B) trimethylolpropane-tri-pelargonate (C) trimethylolpropane-tri-caproate (D) diethylpropanediol- 1,3 di- (3 ,5, trimethylhexanate) (1) tetra-n-butyl-orthosilicic acid-ester (2) tetra-3,5,5-trirnethylheXyl-orthosilicic acid-ester (3) tetra-isotridecyl-orthosilicic acid-ester TABLE I Density viscosity in 051;. at 0. Setting Flame Molecular Viscosity point point Ester weight d4 98.9 37.8 40 54 index 0.)

1, 116 0. 933 5. 49 24. 0 3, 300 15, 900 166 70 255 1, 130 0. 936 5. 6 24. 2 3, 300 15, 800 168 69 258 1, 116 0. 918 9. 9 49. 0 11, 000 61, 100 154 63 257 1, 186 0. 954 10. 4 55.0 11, 900 66, 000 150 61 260 1, 032 0. 948 5. 71 23. 6 2, 520 11, 050 173 70 242 1, 046 0. 946 5. O5 21. 9 2, 715 13, 250 168 -70 246 1, 200 0. 934 8. 9 46. O 7, 680 35, 800 151 65 262 1, 200 0. 925 5. 85 26. 2 3, 040 35, 000 163 63 260 1, 214 0. 923 5. 93 27. 0 4, 360 25, 000 161 -67 267 1, 228 0. 934 7. 8 38. 0 6, 600 36, 300 154 -64 270 1, 228 0. 961 18. 0 100. 0 50, 500 147 52 265 1, 270 0. 943 11. 3 57. 5 15, 100 88, 000 152 58 275 1, 186 0. 974 10. 7 56. 0 150 150 -54 262 1, 214 0. 910 5. 24. 7 6, 380 72, 000 153 65 268 1, 268 0. 968 6. 1 26. 5 4, 800 24, 000 167 65 272 426 0. 917 3. 28 12. 5 1, 372 10, 150 152 71 232 554 0. 943 4. 6 21. 8 6, 010 145 59 278 428 0. 974 3. O 12. 3 2, 085 15, 400 110 65 232 412 0. 914 3. 88 20. 0 18, 800 92 57 220 320 0. 896 1. 04 1. 85 12. 0 51. 0 230 -127 78 600 0. 879 3. 4 12. 78 850 5, 400 161 76 219 824 0. 875 6. 6 36. 0 21, 40 135 52 262 (VI) trimethylolpropane-monopivalate-di-orthosilicatehexa-n-octyl-ester (VII) trimethylolpropane-mono-isobutyrate-di-orthosilicate-di-n-nony1-di-n-decyl-di-n-undecyl-ester The following Table 11 gives the results of various tests run on the same compounds as set forth in the foregoing Table I with respect to their utility as lubricants.

Boiling behavior DIN 51751, 51567 boiling temperature C C.) Evaporation TABLE II Lubricating action Oxidation test Attrition values in the four ball apparatus at 200 C. and a load of 40 kg., scratch diameter in mm.

at torr value, per- Numerical after cent by character- 1 0. 01 760 weight istic 1 h. 2 h. 3 h

255 199 468 1. 30 240 1. 36 1. 54 1. 72 262 204 475 1. 12 217 1. 1. 56 1. 70 257 200 470 1. 2 238 1. 33 1.48 1. 66 267 211 483 1. 54 288 1. 35 1. 51 1. 66 238 181 447 2. 02 282 l. 1. 59 1. 85 244 186 454 2. 0 262 1. 44 1. 63 1. 83 272 216 488 0. 5 225 1. 31 1. 51 1. 64 270 213 485 0. 8 207 1. 26 1. 42 1. 65 274 218 490 0. 77 181 1. 25 1. 43 1. 58 279 223 495 0. 9 219 1. 25 l. 1. 60 277 221 493 1. l 245 1. 27 1. 44 1. 67 288 231 505 1. 17 287 1. 25 1. 41 1. 62 264 208 480 0. 7 210 1. 26 1. 41 1. 61 274 218 490 1. 3 233 1. 32 1. 52 1. 65 284 226 500 1. 1 275 1. 26 1. 58 1. 222 165 428 2. 1 536 1. 6 1. 88 2. 1 258 194 462 1. 6 320 1. 51 1. 72 1. 220 163 425 1. 420 1. 6 1. 78 1. 9 205 410 2. 06 468 1. 65 1. 85 2. O 102 283 12. 2 1, 363 2. 27 223 166 430 6. 5 507 1. 95 2. 3 300 242 518 3. 5 328 1. 58 1. 83 2. 05

1 Oil evaporated.

(VIII) trimethylolethane-monopivalatedi-orthosilicatehexa-n-decyl-ester (IX) trimethylolpropane-mono-pivalate-di-orthosilicateheXa-n-decyl-ester (X) trimethylolpropane-mOno-5,5-dimethylbutyrate-diorthosilicate-hexa-n-decyl-ester (XI) trimethylolpropane-niono-caproate-di-orthosilicatehexa-n-decyl-ester The esters of the invention having molecular weights above 1000 boil at temperatures above 450 C. at 760 torr, above 250 C. at 1 torr and above 180 C. at 0.01 torr. Their flame points range above 260 C.

The viscosity-temperature-responsivity of the esters of the invention determined according to the viscosity index of Dean and Davis (DIN 51 563, see G. V6gtle, Lexikon der Schmierungstechnik, Stuttgart, 1964) is low. Diorthosilicic acid esters wherein A consists of a radical of a trimethylolethaneor trimethylolpropane-pivalic acidmono-ester distinguish themselves from esters with equal R-groups, but other acid components in the A-group by their lowest viscosity and their highest viscosity index.

Due to their viscosity range, the esters according to the invention exhibit outstanding low temperature characteristics. The setting points set out in Table I depends on their viscosity and are not caused by solid deposits.

The thermal stability of the esters was determined by the following test:

300 ml. of the ester to be evaluated (containing 1 percent by weight phenothiazine as oxidation inhibitor), were contacted with 5 l. air/hour at 200 C. (il) for 32 hours. The vaporization value is equal to the amount of liquid products split oii expressed in percent by weight. The numerical characteristic indicates the amount and the nature of the volatile oxidation products and renders a differentiated characteristic of the oxidation tendency of the esters possible. It corresponds to the sum of the weights in mg. of the carbon dioxide evolved during the oxidation and of the organic acids in the condensed, liquid oxidation products respectively.

The oxidative stability of the di-orthosilic acid esters according to the invention was evaluated in comparison with that of dibasic esters and orthosilicic acid esters known in the art. Ester A is illustrative of lubricants which can be employed in the subsonic range. Those lubricants are distinguished by outstanding low temperature characteristics and favorable viscosity indices, but possess only low oxidative stability. Ester B and ester D are typical for lubricants to be used in the supersonic range up to Mach 2.2. Their oxidative stability is good but their viscosity indices and low temperature characteristics are unsatisfactory. From Table I, it is seen that the di-orthosilicic acid esters according to the invention possess the excellent low temperature characteristics as well as viscosity-temperature-responsivity as the ester A comparable therewith in combination with a good or even better oxidative stability as the illustrative esters B to D. As can further be seen from Table II, orthosilicic acid esters (esters 1 to 3 given as example) yield too high evaporation values at the oxidation test.

The esters according to the invention are surprisingly heat-stable; no gel formation occurs by heating above 300 C. in the presence of air. They are also water-resistant.

The esters according to the invention exhibit further good lubricating action. Differentiated numerical characteristics therefor were determined by the attrition test with the four-ball apparatus of Boerlage (Lexikon der Schmiertechnik, G. Vogtle, Franckhsche Verlagshandlung, Stuttgart, 1964) at 200 C. under a constant load of 40 kg. dependent upon the testing time (after 60, 120 and 180 minutes). The four-ball apparatus was heated in an electrically heated metal bath. The oils to be tested were inhibited against oxidation by addition of 1 percent by weight of phenothiazine. The diameters of the scratches thereby obtained (mm.) were determined by microscopic inspection. In comparison to the esters A to D known in the art, the esters according to the invention yielded the lowest attrition values after 60, 120 and 180 minutes. Further, the small rates of growth of the attrition values demonstrate the efficiency of the esters according to the invention as lubricants.

Due to their viscosity, the esters according to the invention can be admixed with other lubricants known in the art in any ratio whatever. Particularly, they are ad mixed with up to 75 percent other lubricants as for instance with mineral lubricating oils, carboxylic acid esters,

organosilicon compounds of various structures (different from those of this invention, polyphenyl-ether-oils or with phosphoric acid esters. Due to their oxidative and thermal stability, lubricating power and viscosity characteristics, including their flowability at low temperatures, the esters according to the invention improve the properties of the added lubricants.

Due to their viscosityand low temperature-characteristics, the heat-stable esters according to the invention can be used as desirable lubricating components for stabilized dibasic esters with quaternary carbon atoms whose viscosity indices alone are unsatisfactory.

What is claimed is:

1. Synthetic lubricants comprising diorthosilicic acid esters of the formula wherein A represents a radical selected from the group consisting of esters of trirnethylolalkanes having a quarternary carbon atom and comprising a total number of up to about 10 carbon atoms and at least one saturated monocarboxylic acid having about 3 to 20 carbon atoms corresponding to the structural formula:

NO-O- wherein Z is the ester residue of said acid and said monocarboxylic acid and R" is a member selected from the group consisting of hydrogen and alkyl having up to 6 carbon atoms, R represents alkyl groups having about 4 to 20 carbon atoms, R represents n-butoxy-diethyleneglycol-ether radical, and n is 0 to 3.

2. Synthetic lubricants according to claim 1, wherein A represents monoesters of an alcohol selected from the group consisting of trimethylolethane, trirnethylolpropane and trimethylolbutane, with an acid selected from the group consisting of pivalic acid, isobutyric acid and fl,fl-dimethylbutyric acid.

3. Synthetic lubricants according to claim 1, wherein said alkyl groups have about 7 to 20 carbon atoms.

4. Synthetic lubricants according to claim 1, containing up to percent conventional lubricating oil.

5. Synthetic lubricants according to claim 1, containing at least one anti-oxidant.

6. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-monopivalate-di-orthosilicate-hexa-n-nonyl-ester.

7. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolethane-monopivalate-di-orthosilicate-hexa-n-nonyl-ester.

8. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-monoisobutyrate-di-orthosilicate-hexa-n-nonyl-ester.

9. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-monopelargonate-di-orthosilicate-hexa-n-nonyl-ester.

10. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolethane-mono pivalate-di-orthosilicate-hexa-n-octyl-ester.

11. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-monopivalate-di-orthosilicate-hexa-n-octyl-ester.

12. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-monoisobutyrate-di-orthosilicate-di-n-nonyl-di-n-decyl di nundecyl-ester.

13. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolethane-monopivalate-di-orthosilicate-hexa-n-decyl-ester.

14. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-monopivalate-di-orthosilicate-hexa-n-decyl-ester.

15. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-mono- [3,5-dimethylbutyrate-di-orthosilicate-hexa-n-decyl-ester.

16. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-monocaproate-di-orthosilicate-hexa-n-decyl-ester.

17. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-mono- 3,5,S-trimethylhexanoate-di-orthosilicate-hexa n decylester.

18. Synthetic lubricants according to claim 1, wherein said diorthosilicic acid ester is trimethylolpropane-monopropionate-di-orthosilicate-heXa-ndecyl-ester.

19. Synthetic lubricants according to claim 1, wherein said diorthosilicic acid ester is trimthylolpropane-monopivalate-di-orthosilicate-hexa-iso-decyI-ester.

20. Synthetic lubricants according to claim 1, wherein said di-orthosilicic acid ester is trimethylolpropane-monopivalate-di-orthosilicate-tri-n-undecyl tri (diethyleneglycol-n-butyl-ether) -ester.

References Cited UNITED STATES PATENTS Abbott, et al 260448.8 Shibe 260448.8

Abbott, et al 260448.8 Smith, et al. 260448.8 Wheeler 260448.8 Wong, et al. 260448.8 XR Kearney 260448.8 XR Gothel, et al. 260448.8 XR

Gothel, et al. 260448.8 XR

US. Cl. X.R.

23 g 1 I UNITED STATES PATENT OFFICE I 2 ----CERTIFICATE OF CORRECTION Patent No. 3514402 Dated MAY 26. 1970 luv-winds) Herbert Gothel et a1 '1,

r and that said Letters Patent are hereby corrected as shown below:

Columnfl, line 3 of Abstract" (Sp e e; p J1," lline' 3 of Abstract) Formula: "(Si D A Si)" Should be (Si 0 -t r 0 It is certified that error appeare in the above-identified patent v Column 5 2 line 7 (Spec pt 10, line v "depends" should be depend- .Colunni 5, line 70 (Spec. p-. 12, line 20.

Close parenthesis after "invention" SIGNED AND SEALED -novzngm I 0mm Oomniaaionor t 

